1. Field of the Invention
The present invention relates to a refrigeration circuit for transferring heat energy between two regions. More particularly, the present invention concerns a movable expansion device for use with a reversible refrigeration system, said device having a piston with a metering port and means as set forth herein for adjusting the throttling of refrigerant through that metering port.
2. Description of the Prior Art
In a typical vapor compression refrigeration circuit various components such as a compressor, condenser, evaporator and expansion device are arranged to transfer heat energy between a fluid in heat transfer relation with the evaporator and a fluid in heat transfer relation with the condenser. In a heat pump system, an outdoor coil and an indoor coil are located such that the compressor, through a reversing valve, may direct hot gaseous refrigerant to either coil acting as a condenser. The other coil then acts as an evaporator such that depending upon the position of the reversing valve, heat energy is either rejected or absorbed in both the indoor or the outdoor coil. In the heating mode of operation, heat is rejected in the indoor coil acting as a condenser and heat is absorbed in the outdoor coil acting as an evaporator. The reverse is true in the cooling mode of operation wherein the heat is rejected at the outdoor coil acting as a condenser and heat is absorbed at the indoor coil acting as an evaporator.
Since the operating conditions of a heat pump unit depend upon whether it is in the heating mode of operation or the cooling mode of operation, it is known to utilize an expansion device associated with each mode of operation. The conventional method of accomplishing this was to incorporate two subassemblies each including an expansion device such as thermal expansion valves or distributor and capillaries in parallel with a check valve. Each assembly is associated with a particular heat exchanger such that regardless of the mode of operation the refrigerant flows from the condenser to the evaporator. When the heat exchanger with which the assembly is associated is serving as a condenser, liquid refrigerant flows through the check valve bypassing the expansion device. When the heat exchanger associated with the assembly is acting as an evaporator, the refrigerant may not flow through the check valve but instead is forced to flow through the expansion device into the coil.
A combination device is disclosed in U.S. Pat. No. 3,992,898 issued to the assignee hereof. This patent discloses a piston mounted in a valve body, the piston having a metering port running through the center thereof and fluted channels defining a bypass region between the exterior of the piston and the valve body. This arrangement provides for throttling of the refrigerant through the orifice for expansion purposes when refrigerant flows in one direction and for allowing bypass of the refrigerant around the exterior of the piston as well as through the metering port when refrigerant flows in the other direction such that the free refrigerant flow may be had therethrough. Thus, a single device provides for the expansion of the refrigerant when the coil associated therewith is acting as an evaporator and for allowing free flow of the refrigerant therethrough, similar to the flow through the check valve, when the coil associated therewith is acting as a condenser.
It has further been known to incorporate in refrigeration and air conditioning units where the heat exchangers are sufficiently close in distance a single body having two pistons such that the expansion device associated with each heat exchanger is combined into one device having a piston associated with each heat exchanger.
Utilizing these movable expansion devices as set forth in the patent provides a economical, safe and efficient means for providing the combined operation necessary in a heat pump system. The system may be adjusted as to the amount of refrigerant superheat and other expansion parameters by changing the piston located within the valve body. The piston usually is changed to vary the diameter of the metering port running the length of the piston. Consequently, the pressure drop through the piston when it is serving as an expansion device may be varied. Naturally, to uncouple the expansion device to remove the piston requires that the refrigeration circuit of the system be unsealed and that the necessary steps involved with field repair when the refrigerant circuit is opened be taken. These steps include pumpdown of refrigerant, inserting a filter-drier to remove the unwanted contaminants and posing the risk of contaminants entering the system limiting the design life of the components of the system.
The present invention concerns an improvement of this movable expansion device by providing means for adjusting the diameter of the metering port extending the length of the piston without having to break into the refrigeration circuit of the system and consequently without incurring the potential injuries and side effects to the refrigerant circuit caused by interrupting the integrity thereof. This means for adjusting will further provide the serviceman with a method of fine tuning the operation of the refrigerant circuit without unsealing the circuit.